The invention relates to a spring unit for the weight setting of a chair, in particular an office chair, having a first spring element and at least one further spring element. In this case, weight setting is understood to mean the setting of the opposing force to be applied by the spring unit to the weight of the person using the chair.
For the weight setting of a chair, DE 38 34 614 A1 discloses the provision of a spring unit which has a gas spring and a spiral spring which surrounds the latter coaxially and is borne by the gas spring, which is held on the chair frame at one end such that it can rotate. The construction and the mode of action of a gas spring of this type is described, for example, in DE 42 37 495 A1.
In the known spring unit, the prestress of the spiral spring, which acts as a compression spring, is set manually by means of a rotary knob coupled to a sleeve-like driver. The drawback in this case is that, on the one hand, in particular in the case of a permanent maximum weight setting, the spiral spring serving as a compression spring is often kept in the prestressed state to an undesirably high extent and/or over an impermissibly long time period. On the other hand, with a high expenditure of force, which at the same time is undesirable, a large number of revolutions of the rotary knob are needed for the weight setting, so that in the event of a bodily posture which is generally unfavorable, said setting is very time-consuming, because of the often poor accessibility of the rotary knob.
The invention is therefore based on the object of specifying a spring unit of the type mentioned at the beginning which, while avoiding the aforementioned disadvantages, permits a particularly suitable weight or force setting of a chair over the greatest possible force range. The spring unit is in particular to be suitable for an easy-to-handle weight setting of an office chair provided, for example, with a synchronizing mechanism for adjusting the inclination of a backrest/seat unit.
According to the invention, this object is achieved by the features of claim 1. To this end, provision is made that at a basic setting, preferably for a minimum opposing force to be applied by the spring unit to the weight, only the first spring element is effective. In order to increase the opposing force of the spring unit adjustably, a number of further spring elements can be connected up, individually or in combination in steps, to the first spring element, which is preferably a gas spring. As a result, depending on the set weightxe2x80x94and therefore as a function of the opposing force to be applied by the spring unit to the weightxe2x80x94at least one of the further spring elements is effective in addition to the gas spring. At the same time, both the gas spring and the connected-up spring elements are effective only under load, that is to say when a compressive force or weight is exerted on the spring unit. In other words: when the spring unit is not loaded, in particular none of the connected spring elements is prestressed.
In an advantageous refinement of the spring unit, both the first spring element and the or each further spring element are a gas spring. In this case, the gas springs are jointly held on one side by their housing-side spring ends. Their piston-side spring ends can then expediently be brought into operative engagement, individually or in combination, with an adjusting slotted guide. The gas springs of the spring unit can be arranged beside one another both in a row and in a circle. The adjusting slotted guide can be designed as a perforated slide or as a perforated, rotatable disk. Both the perforated slide and the perforated disk can be provided with a latching mechanism. In this case, the slide or the disk latches in various positions in such a way that the respectively inactivated gas springs slide with their piston-side ends through the holes which are aligned with the latter when no weight is acting on the spring unit.
In an alternative embodiment, the or each further spring element is a spiral spring surrounding the gas spring coaxially. In this case, a first spiral spring surrounding the gas spring and a second spiral spring surrounding the first are expediently provided, between which a distance sleeve can be arranged. The inner, first spiral spring is in this case preferably weaker than the outer, second spiral spring.
In order to connect up the spiral springs to the gas spring, their movable piston end is guided on a cross-shaped arm, on which two plunger arms are arranged such that they can be displaced synchronously and transversely with respect to the spring axis. Depending on the set position of the plunger arms, these either slide past the outer spiral springsxe2x80x94only the gas spring then being effectivexe2x80x94or are in an active position with the outer spiral spring, with the inner spiral spring or with both spiral springs.
The advantages achieved with the invention consist in particular in that, as a result of the use of a spring unit expediently having one gas spring as a first spring element for the basic weight setting and having a number of further spring elements which can be connected up individually or in combination to the gas spring, a stepwise setting of the opposing force of the spring unit, and therefore a stepwise weight setting of a chair is possible in a particularly simple way.
The spring unit is particularly suitable for the weight setting of an office chair having a synchronizing mechanism for adjusting the inclination of the backrest or of the latter in a unit with the seat. In this application, the spring unit is expediently arranged between a seat carrier that is connected to a rotary column, and the seat. Alternatively, the spring unit can also be arranged between the seat carrier and a backrest link which extends at least approximately parallel to the seat or to the seating area and belongs to the backrest.